I was thinking of buying this (first AMP) for my newly purchased Beyerdynamics T1. But reading last couple of posts... would it best for me to get a 'high impedance' amp, despite this being a very good price?

It has a voltage mode which will work on all headphones. As for using current mode with non linear impedance headphones (not high impedance, it's just that high impedance cans tend to not have flat impedances), your mileage may vary.